Electron discharge device



Sept. 15; 1942.

F. .1. G. VAN DEN BOSCH 2,295,919

ELECTRON DISCHARGE DEVICE FiledMay 20. 1940 38 2 1 -10 2452/ va J 38 5 37 mvzu'rok EJ. VAN DEN Boscr-i W'- M Ar Patented Sept. 15, 1942 U NTTED" STATES i F F'lC'EZ p ELECTRON DISCHARGE DEVICE" Francois Joseph Gerard van, den Bosch, Hurley; England, assignor to VacuumwScience Products Limited, London, England, aBritishcompany Application-May 20, 1940; Serial-No. 336,308

In Great Britain May 25', 1 939 3 Glaimsi Thisv invention relates to electron-discharge devices comprising an'electrode assembly having one or more electrodes employedfor the purpose of producing a secondary electron emission,- in order to obtain electron multiplication. Usually, such electron multiplication assembly: comprises a primary cathode, one or more secondary cathodes and a collector enclosed in an envelope and so arranged that electrons emitted by the primary cathode are caused to impinge onthe secondary cathode and liberate other electrons which impinge on the next secondary cathode, when more than one, and so on in succession to the collector.

According to the present invention there is provided an electron-discharge device comprising the combination of an electron multiplier electrode assembly and one or more additional electrode assemblies for operation other than with electron multiplication, and. having a single thermionic cathode structure common to the electrode assemblies. Thus, there may be one or more additional electrode assemblies comprising adjacent to th cathode structure an anode to form a rectifying diode or with one or more additional electrodes to provide a triode or multielectrode valve. assembly for operation as: an amplifier or oscillation generator.

A further feature of the invention consists in that the cathodestru'cture comprises: a plurality of cathode elements and a single heater common to said cathode. elements. Thus, each electrode assembly may have itsown cathode element In one construction the cathode structure comprises a tube having an enlarged disc-like end provided with an emissive surface constituting. the cathode element of the electron multiplier assembly and an. emissive surface. on the exterior of the. tube constituting the cathode element, or elements, of the one or. more additional electrode assemblies.

Another feature of the invention consists in the provision of a screen shielding electrodes of the electron multiplier assembly from electrodes of the one or more additional electrode assemblies. In one form this screen surrounds the one or more additional electrode assemblies and has an opening for the aforesaid disc-like cathode element of the electron multiplier assembly.

The invention includes a homodyne or frequency-changing apparatus comprising an electron-discharge device as aforesaid in which two control electrodes are provided in the electron multiplier assembly, in combination with a circuit connected to the additional electrode assemblyfor producing therewith local oscillations, an electrical connection or coupling for feeding the local oscillations and one of said control electrodes; means for applying signals to the other or said control electrodes and means for extracting an output from the collector of the electron multiplier assembly.

One specific construction of electron discharge device according to the inventionisshown diagrammatically and by way of example in the accompanying. drawing.

eferring' to Figure 1 of. the drawing, the cathode structure comprises ametal tube I!) having: an enlarged disc-like part II. at one end. Theouter surface. of this. disc-like part is provided. with a coating 28; freely emitting electrons, suchas a, coating. of barium oxide. or strontium oxide, and: constitutes the cathode. element of the electronmultipli'er assembly. The electron emission from this cathode element is. controlled by two. grid electrodes '12 and 13 between which there. is. provided. another electrode 14' in the form of a. platewith a single. aperture. through which the. electrons are directed towards a secondarycathode t5. The secondary cathode I5 is an apertured electrode consisting. of a perforated plate; for: instance, as described in they specification of United States; application No. 276,883, filed June. 1,, I939; but it may alternatively be constituted by a wire grid ormesh. Other secondary cathodes similar to; the secondary cathode I15 are provided, as; indicated at I6, I11, l8 and I9; with a final secondary cathode: 2,0 of'disc form and a collector'electrode 2|- in. the form of a grid interposed between the secondary cathodes: l9

and 20-. The secondary cathodes. I6, ll, I8 and l9 are each provided with an auxiliary electrode 22 to the front; as. described in the specification of, United States. application No.. 326,813; filed March: 29 i940, and connected electrically to. the secondary cathode.

The tube l0 also has a second emissive coating 29 surrounded by a cylindrical grid electrode 23 and a cylindrical anode 24 together constituting a thermionic triode.

A heating element 9 is provided within the tube H] for indirectly heating the tube and thus the cathode elements provided by the emissive coatings on the tube. It is convenient to operate the cathode element providing the emission for electron multiplication at a lower temperature than the other cathode element, so that the heater preferably does not extend fully to the disc-like part II. For instance, the heater may be arranged to lie within the tube I0 only ad- .iacent that part which has the emissive coating for the triode assembly.

Around this triode assembly there is provided a cylindrical screen 25 formed of a wire grid or mesh. This screen has an end member 26 having an opening 2'! in which the disc-like cathode element 1 I of the multiplier assembly is located. The disc-like cathode element ll may be a close fit in the opening 21 and the screen is electrically connected to the tube ll of the cathode structure. The cylindrical screen 25 may be formed by a metal tube instead of a grid or mesh. I

One application of this electron-discharge device is as in frequency-changing apparatus, for instance in a radio receiver of the super-heterodyne type. In this case the thermionic triode assembly is connected with an external circuit indicated at 30 in known manner for producing, with the triode, local oscillations. These local oscillations are fed to the control electrode I 3 of the electron multiplier assembly and to the control electrode l2 the incoming signals are applied direct or through a preselecting amplifier 3|. A mixing of the local oscillations and applied signals is thus obtained and subsequent amplification is produced through the several multiplier stages of the electron multiplier assembly. Progressively increasing potentials positive with respect to the cathode element ID are applied to the accelerator M, the secondary cathodes l5, I6, 11, I8, l9 and 20 and the collector 2! through the resistance potentiometer 35. The amplified. output at intermediate frequency may thus be applied to a tuned intermediate frequency circuit 32 from the collector electrode 2| and utilized in any known manner for the reproduction of the signals. Thus the intermediate frequency signals from the circuits 32 may be applied to a detector 33, followed by an output signal amplifier 34. The electron-discharge dev ce may similarly be used in a homodyne circuit.

The electron multiplier assembly is provided with operating potentials in known manner in that the secondary cathodes l to 20 and the 001- lector 2| are provided with progressively increasing positive potentials with respect to the cathode tube l0 and the electrode I4 is also operated at a potential which is positive with respect to the cathode tube H] but generally lower than that of the first secondary cathode [5.

It is to be understood that the invention is not restricted to the specific construction here inbefore described with reference to Figure 1. For instance, a plurality of additional electron assemblies may be employed having cathode elements spaced apart lengthwise of the tube l0 and comprising two or more electrodes.

In the modification shown in Figure 3 the tube 10 is extended and has an additional coating 36 freely emitting electrons, around which there is mounted a tubular anode 31, to form a thermionic diode. In this case the cylindrical screen 25 is extended to surround the diode and a metal disc 38 is provided across this screen between the diode assembly and the triode assembly.

In Figure 3 a modification of the metallic end member 26 is shown in which this member is formed with a small opening 21 through which the tube I0 passes with the disc-like element ll situated above this end member. In this case a short tube 39 is provided around the disc-like element II and is secured to the end member 25 of the screen.

I claim:

1. An electron discharge device comprising an electrode assembly for electron multiplication and an additional electrode assembly for operation other than by electron multiplication, said electrode assemblies having a single thermionic cathode structure common to them both, which cathode structure comprises a tube with an enlarged end part, an electron emissive layer on said end part for said electrode assembly for electron multiplication, an electron emissive layer on said tube and spaced from the end part and constituting an electron emissive surface for said additional electrode assembly and means for indirectly heating said cathode structure.

2. An electron discharge device comprising an electrode assembly for electron multiplication and an additional electrode assembly for operation other than by electron multiplication, said electrode assemblies having a single thermionic cathode structure common to them both, which cathode structure comprises a tube with an enlarged end part, an electron emissive layer on said end part for said electrode assembly for electron multiplication, an electron emissive layer on said tube and spaced from the end part and constituting an electron emissive surface for said additional electrode assembly, means for indirectly heating said cathode structure and a screen around said additional electrode assembly and having an opening receiving said enlarged end part carrying the electron emissive layer for the electrode assembly for electron multiplication.

3. An electron discharge device comprising a plurality of electrode assemblies, said electrode assemblies having a single thermionic cathode structure common to them, said cathode structure comprising a tube with an enlarged disclike end part, an electron emissive layer on said end part for one electrode assembly and another electron emissive layer on said tube and spaced from said end part for sembly.

FRANCOIS JOSEPH GERARD VAN DEN BOSCH.

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